Selecting the Proper Lead-Acid Technology WHITE PAPER

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Selecting the Proper Lead-Acid Technology Introduction With so many different battery technologies on the market today, it can be difficult to make sure you’re selecting the right battery for your application. This document will describe the basic types of lead-acid batteries available, and help you understand which one will provide the best performance and value for your needs. Basic Battery Types Flooded (Wet) The flooded lead-acid (FLA) battery, invented in 1859, was the first Figure 1: Construction of a Flooded Battery rechargeable battery. After decades of refinement, it remains the primary choice for many applications. The battery plates are immersed in an electrolyte Built-in lifting brackets Anti-flame propagation of dilute sulfuric acid, and removable caps in the lid allow replacement of vent caps lost water. FLA batteries are cost effective, rugged, and provide reliable Low profile terminals performance when properly maintained. True deep-cycle construction Because FLA batteries are not sealed, they must be kept in the proper Proprietary Maxguard® orientation (upright) to avoid spilling of electrolyte. Due to the risk of spills, advanced design separator they cannot be shipped by air. Robust plate design

During the charging process, FLA batteries consume water and release Trademarked maroon case hydrogen gas, which must be properly vented to avoid potential fire hazards. Trojan’s unique The water consumed during charging must periodically be replaced at a Alpha Plus™ Paste frequency that varies with the usage profile. Although the introduction of single-point watering systems has reduced the overall effort to water FLA batteries, this periodic requirement means that these batteries are appropriate only in situations where regular maintenance can be assured. With proper maintenance and charging, flooded batteries can provide years of reliable service in many applications. Absorbed Glass Mat (AGM) The AGM battery is a sealed battery that fits into the category of Valve- Figure 2: Construction of an AGM Battery Regulated Lead Acid (VRLA) batteries. These batteries are designed so that hydrogen and oxygen are recombined within the battery, rather than being vented. A built-in valve will release excess gas in case of a severe overcharge. An AGM battery is constructed by compressing a glass fiber mat between each plate. The glass mat holds electrolyte in place much like a sponge, and Glass Mat Separator helps support the plates. This gives AGM batteries good resistance to shock Lead/Lead Oxide and vibration. Heavy-Duty Grid Since AGM batteries are sealed, they can be mounted on their sides if desired High-Density Paste and ventilation requirements are much less demanding than with flooded batteries. They can be shipped by air if needed. They have the ability to charge Thick-Walled and discharge at high rates and perform well at low temperatures. Polypropylene Case It is very important that AGM batteries not be severely overcharged, as this will cause the battery to rapidly dry out. The selected charger must specifically have an AGM setting to avoid damaging the battery. Gel A Gel battery is another type of VRLA battery, and like the AGM, is sealed. Although Figure 3: Trojan 102 Ah Gel Battery the basic internal construction of a Gel battery is similar to that of the flooded battery, the electrolyte has been immobilized by the addition of a thickening agent, taking on the look and consistency of petroleum jelly. Like the AGM, it can be mounted on its side and doesn’t release hydrogen during normal operation. Gel batteries have a higher initial cost, and typically don’t work as well in higher power applications. In deep-cycle applications, they will generally outlast an AGM battery, unless the AGM has been designed for deep cycling. Like the AGM, the selected charger must have a specific Gel setting to avoid overcharge damage. Additionally, the charger and charge algorithm should support temperature- compensated charging. Since Gel batteries are resistant to spills and leakage, they can also be shipped by air.

Key Performance Characteristics Self-Discharge Now that we’ve described the basic categories of lead-acid batteries, Self-discharge is the capacity loss that occurs within a battery let’s take a look at the various performance characteristics that may even when it is not connected to a load. How quickly a battery self- come into play as you select the proper battery for your application. discharges is related to temperature, where warmer temperatures Sealing/Gas Release mean the battery will self-discharge quicker. A result of parasitic chemical reactions within the battery, the self-discharge rate of VRLA As previously noted, the process of charging a lead-acid battery batteries is much lower than that of FLA batteries. This can be an generates hydrogen and oxygen. In a flooded battery, these gases important constraint if batteries need to be stored for long periods are released to the external atmosphere. In a VRLA battery, these of time. gases are internally recombined and stay within the battery. In some applications, the required ventilation requirements for a Low-Temperature Performance flooded battery are not feasible. In others, the possibility of acid Some applications require batteries to perform well even at leaks during service or due to a broken case are unacceptable. temperatures well below 0°C (32°F). AGM batteries have the best This guides the selection process to one of the VRLA types. low-temperature performance of the three technologies discussed here. Maintenance Flooded batteries require regular water replacement to continue to Energy Density perform effectively. If regular maintenance cycles to add water are Within the lead-acid family, FLA batteries have the most capacity impractical, such as in remote, unstaffed installations, then one for a given size or weight. When you need the most Ah possible in a of the VRLA technologies may be more desirable. Note that even size-constrained location, then flooded batteries are likely your best though VRLA batteries don’t require watering, periodic cleaning and choice. re-torqueing of connections is still required. Power Density Deep-Cycle Capability AGM batteries are best suited in applications where high discharge Flooded and VRLA batteries, when designed for deep cycling, have currents are needed. Gel batteries are more suited to longer, lower- very good cycling capability. While flooded types typically have very current cycles. At high rates of discharge, AGM batteries deliver more good cycling, they require proper maintenance in order to achieve of their theoretical capacity than do FLA batteries. long cycle life. VRLA types do not require maintenance but do require Round-Trip Efficiency proper charging in order to achieve long cycle life. Whenever energy is converted and stored, there will always be an Recharge Time efficiency penalty. The round-trip efficiency, or the percentage of FLA batteries need a higher amount of overcharge than VRLA types energy that a battery delivers compared to the energy that it took to avoid a harmful effect known as stratification, so this can extend to charge it, can be particularly important in certain applications. FLA charge times. However, charge time is more dependent upon the FLA batteries typically have round-trip efficiencies of 70-80%, while depth of discharge and the size (power) of the charger being used. VRLA batteries will be in the range of 80-90%. Cost Due to the cost of materials and processing, FLA batteries are generally the least expensive, while Gel batteries are the most expensive. AGM batteries will fall somewhere in between. Summary As this paper has described, a wide variety of factors can influence the selection of the proper lead-acid battery technology. In some instances, one particular factor may dominate the decision, while in others a mix of performance attributes may determine which technology will be the best. The table below summarizes the various factors that have been discussed in the previous sections. For additional information, you may contact Trojan technical support at [email protected].

SUMMARY TABLE

Flooded Lead Acid VRLA - AGM VRLA - Gel

Not sealed – will release H2 Low to no gassing Low to no gassing Sealing/Gas Release and O2 during charging unless overcharged unless overcharged

Spill-proof/Leak-proof No Yes Yes

Mounting Flexibility Must be upright Upright or on side Upright or on side

Requires periodic water Maintenance Maintenance-free Maintenance-free replacement

Deep-Cycle Capability Best Better Better

Recharge Time Longer Shorter Long

Self-Discharge Up to 15% per month 1-3% per month 1-3% per month

Low-Temperature Good Best Fair Performance

Energy Density Highest Lower Lower

Power Density Medium High Low

Round Trip Efficiency 70-80% 80-90% 80-90%

Cost Low Medium High

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